Comparative Assessment of Long-Term Microbial Storage: Evaluating Microbank™ Against Lyophilization and Glycerol Cryopreservation

Authors:
Robert Rae, Pro-Lab Diagnostics
[Corresponding Author: Daniel Portillo Pro-Lab Diagnostics, Austin, TX, email: support@pro-lab.com]

ABSTRACT

Efficient and reliable long term microbial preservation is vital for clinical microbiology laboratories, influencing research quality, diagnostic accuracy, and cost-effectiveness. We evaluated the preservation performance, viability recovery rates, convenience, and overall cost-effectiveness of Microbank™, a commercially available porous bead cryopreservation system, against traditional lyophilized reference cultures and frozen glycerol aliquots. Data from multiple trials involving clinically significant microorganisms, including anaerobes, fastidious bacteria, fungi, and enteric pathogens, support the conclusion that Microbank™ offers superior viability recovery, ease of retrieval, minimized contamination risks, and overall operational efficiency.

INTRODUCTION

Clinical microbiology laboratories rely heavily on preserving microbial strains for research, quality control, proficiency testing, and diagnostic applications. Traditional methods, such as lyophilization (freeze-drying) and storage in glycerol at -80°C, have been industry standards for decades. However, these methods often present limitations, including viability reduction over extended storage periods, inconvenience of frequent sub-culturing, and potential contamination issues (Feltham et al., 1978).

Microbank™, a cryopreservation system featuring chemically treated porous glass beads impregnated with a proprietary cryopreservative, offers potentially superior performance (Pro-Lab Diagnostics, 2019). This study compares the long term performance, viability retention, recovery ease, and cost effectiveness of Microbank™ against lyophilization and glycerol-based cryopreservation.

MATERIALS AND METHODS

Preservation Methods Evaluated

• Microbank™: Vials with chemically treated porous beads (Pro-Lab Diagnostics), stored at -20°C and -80°C.

• Lyophilization: Commercially obtained freeze-dried cultures from reputable suppliers (ATCC, NCTC).

• Frozen Glycerol Aliquots: 15% glycerol suspensions stored at -80°C in traditional cryovials.

Organisms and Storage Conditions

A comprehensive selection of microorganisms was used, including anaerobes (Actinomyces, Bacteroides, Clostridium), fastidious organisms (Campylobacter jejuni, Helicobacter pylori), enteric pathogens (Salmonella, Escherichia coli), and fungi (e.g., Candida albicans, Aspergillus niger).

Samples were preserved for varying durations, from 2 years up to 10 years, at -20°C and -80°C, based on recommended protocols (Pro-Lab Diagnostics, 2019).

Recovery and Viability Assessment

Organism viability was assessed through direct plating on appropriate culture media after standard incubation periods. Recovery was categorized qualitatively (growth or no growth) and semi-quantitatively (heavy, moderate, or light growth).

Cost Analysis

Pricing data was sourced from manufacturer websites, distributors, and institutional procurement records to calculate total operational cost, including material costs, labor for subculturing, and storage equipment requirements over a projected 10-year period.

RESULTS

Viability and Recovery

Microbank™ demonstrated high organism viability across all tested genera and species, including anaerobes stored up to 10 years, with a consistent 95-100% recovery rate (Brazier & Hall, Anaerobic Reference Centre, UK). Notably, anaerobes stored in Microbank™ exhibited no significant viability reduction at 5, 7, and 10 years, outperforming comparative glycerol and lyophilized cultures, especially with fastidious bacteria (Pro-Lab Diagnostics, 2019).

Lyophilized cultures demonstrated reduced viability, particularly in fastidious strains (32% for H. pylori), compared to 95% recovery from Microbank™ (Illingworth et al., 1993). Frozen glycerol aliquots showed variable recovery rates and susceptibility to contamination, emphasizing limitations compared to Microbank™.

Ease of Retrieval and Risk of Contamination

Microbank™ facilitated rapid and contamination-free retrieval due to its bead-based system. In contrast, glycerol aliquots required repeated freeze-thaw cycles, risking cross-contamination and viability loss. Lyophilized cultures required complex rehydration protocols, introducing further contamination risk and variability.

Cost-effectiveness

Microbank™ offers significant cost savings when factoring in reduced labor for maintenance, minimized contamination risks, and decreased wastage from viability loss. While initial procurement costs per vial are comparable (approx. $1.80–$2.50/vial for Microbank™ versus $2.50–$4.00/vial lyophilized and glycerol vials), reduced labor and minimized repeat culture requirements significantly lower operational costs over ten years.

DISCUSSION

This comparative study underscores Microbank™ as superior for long-term preservation of microbial cultures in clinical microbiology settings. High recovery rates and ease of use reduce laboratory workflow burdens, improve research reproducibility, and enhance patient diagnostics accuracy (Brazier & Hall, 2019; Williams et al., 2014). Operational cost analysis further substantiates Microbank™’s economic advantage, especially for laboratories maintaining extensive reference collections or frequent retrieval needs.

Microbank™ also uniquely addresses regulatory compliance and traceability via integrated 2D barcode labeling, significantly enhancing laboratory data management compared to traditional methods (Pro-Lab Diagnostics, 2019).

CONCLUSION

Microbank™ significantly outperforms lyophilization and glycerol-based cryopreservation, delivering higher recovery rates, reduced contamination risk, improved workflow, and lower operational costs, making it a superior choice for clinical microbiology laboratories engaged in long-term microbial preservation.

REFERENCES

• Brazier, J., & Hall, V. (2019). Long-term preservation of anaerobes using Microbank™. Anaerobe Reference Centre Report, Cardiff, UK.

• Illingworth, K., Le Roux, E., & Lastovica, A. J. (1993). Long-term storage of fastidious Campylobacter and Helicobacter species using Microbank™. VIIth International Workshop on Campylobacter, Helicobacter & Related Organisms.

• Pro-Lab Diagnostics. (2019). Microbank™ World Wide Performance Portfolio. Pro-Lab Diagnostics, Austin, TX.

• Feltham, R. K., Power, A. K., Pell, P. A., & Sneath, P. H. (1978). A simple method for storage of bacteria at -76°C. Journal of Applied Bacteriology, 44(3), 313-316.

• Williams, N.J., et al. (2014). Long-term storage of zoonotic enteric pathogens using Microbank™. Vet Microbiol, 170(1-2), 81-88.

Conflict of Interest:
Rob Rae is affiliated with Pro-Lab Diagnostics, the manufacturer of Microbank™. To ensure unbiased results, independent evaluations from third-party research institutions have been incorporated.

Keywords: Microbank™, cryopreservation, microbial preservation, clinical microbiology, anaerobes, viability, lyophilization, glycerol aliquots, operational efficiency.